1. Field of the Invention
This invention relates to digital signal processing circuits, and more particularly, to a variable digital signal processing circuit formed on a single chip which can be used either alone or in combination with other such chips to build more complex digital circuits.
2. Description of the Prior Art
Digital electronics equipment such as, for example, digital color video camera, generally employ a number of discrete digital circuits such as digital filters, matrix circuits, encoder circuits, adding circuits, multiplier circuits, and the like to process digital data. Discrete digital circuits, however, in such equipment possess significant disadvantages. The equipment is generally bulky, since a number of circuits are used in the construction. Second, such digital equipment is generally expensive because specialized chips are made just for one particular application. It is to be appreciated that the unit cost is very high for designing and manufacturing a limited number of digital circuits. Thus, a digital apparatus using discrete digital circuits is often expensive.
A frequent operation that occurs in digital circuits is the addition of the bits comprising the data words. The bits must be added together and the summing operation completed within one clock period. For example, in a digital color video camera, the sequential addition of the bits must be performed within one period of a clock pulse which has a frequency four times as high as the frequency of the color subcarrier signal. Accordingly, the adding circuit must employ high speed logic elements such as transistor-transistor logic (TTL), emitter-coupled logic (ECL) or the like. However, these high speed logic elements prevent the adding circuit from being formed as a chip with a high integration value and low power consumption. On the other hand, while complementary metal oxide semiconductor (CMOS) logic elements have a high integration value and low power consumption. On the other hand, while complementary metal oxide semiconductor (CMOS) logic elements have a high integration value and low power comsumption, they are not conventionally used for calculation logic elements because of their low calculating speed.